The present application claims priority to Japanese Applications No. P11-294406 filed Oct. 15, 1999, which application is incorporated herein by reference to the extent permitted by law.
The present invention relates to an apparatus and a method for producing an optical component by forming a multi-layer film on a base.
To realize good optical characteristics of an optical component comprised of an optical film, such as a dichroic mirror, the optical film is required to be of a multi-layer structure having at least ten optical thin layers. The optical thin layer is formed by a low refractive index material such as MgF2 or SiO2 or a high refractive index material such as TiO2 or Nb2O5. A usual batch process used for producing an optical component comprised of an optical film having a multi-layer structure of optical thin layers involves evaporating raw materials for the optical thin layers in a vacuum system in accordance with a vapor-deposition process or sputtering process, to form the optical thin layers on a transparent member such as a glass board.
One example of a related art method of producing an optical component by forming an optical film having a multi-layer structure of optical thin layers has been disclosed in Japanese Patent Laid-open No. Hei 11-119002.
In accordance with this method, optical thin layers are continuously formed on a base, typically, a film in such a manner that the configuration of the optical thin layers is adjusted to a predetermined optically designed configuration as a whole, by forming the optical thin layers on the base, and simultaneously controlling a thickness of each layer to satisfy a specific light transmission characteristic by using, for example, an optical monitor.
The method disclosed in the above document, Japanese Patent Laid-open No. Hei 11-119002, however, has the following problems: namely, since the method fails in means for accurately measuring a thickness of each of optical thin layers continuously formed on the base such as film, the thickness of the optical thin layer intended to be adjustably formed is, really, inaccurately measured. This gives rise to not only a problem that the optical component produced by this method cannot exhibit ideal optical characteristics due to a deviation of the thickness of each optical thin layer from the ideal thickness, but also a problem that a variation in optical characteristics occurs between optical components produced by this method.
For example, as shown in FIG. 14, when each optical thin layer is formed at a usual formation rate in accordance with the related art method, an optical characteristic represented by a light transmittance is largely changed due to a change in thickness of the optical thin layer. In the figure, values xe2x80x9c74.76 nmxe2x80x9d, xe2x80x9c194.76 nmxe2x80x9d, and xe2x80x9c114.76 nmxe2x80x9d designate the thicknesses of the optical thin layers. Even when each optical thin layer is formed at a formation rate slower than the usual rate in accordance with the related art method, as shown in FIG. 15, an optical characteristic represented by a light transmittance is largely changed due to a change in thickness of the optical thin layer. In the figure, values xe2x80x9c0 nmxe2x80x9d, xe2x80x9c65.5 nmxe2x80x9d, xe2x80x9c97.3 nmxe2x80x9d and xe2x80x9c112.4 nmxe2x80x9d designate the thicknesses of the optical thin layers.
The above related art method has a further problem that since the film thickness adjustment is performed for each of optical thin layers constituting an optical film, it takes a lot of time to form the optical film composed of the optical thin layers.
An object of the present invention is to provide an apparatus and a method for producing an optical component, each of which is capable of easily, stably producing an optical component having good optical characteristics.
To achieve the above object, according to a first aspect of the present invention, there is provided an optical component producing apparatus for forming a multi-layer film, which is composed of alternately stacked layers different in optical characteristic, on a base, the apparatus including: film formation means for forming the multi-layer film on the base; measurement means for measuring an optical characteristic of the optical component obtained by forming the multi-layer film on the base; and control means for controlling a thickness of a portion of the multi-layer film formed by the film formation means on the basis of the measured optical characteristic of the optical component.
According to a second aspect of the present invention, there is provided an optical component producing method for forming a multi-layer film, which is composed of alternately stacked layers different in optical characteristic, on a base, the method including: measuring an optical characteristic of the optical component obtained by forming the multi-layer film on the base; and controlling, on the basis of the measured optical characteristic of the optical component, a thickness of a portion of the multi-layer film to be formed on the base.
With these configurations, layers of a multi-layer film are formed one by one on the base (by the film formation means), wherein an optical characteristic of an optical component obtained by forming the multi-layer film on the base is measured (by the measurement means), and a portion of the multi-layer film formed by the film formation means is controlled (by the control means) on the basis of the measured optical characteristic of the optical component. Here, by selecting a portion exerting the largest effect on the optical characteristic of the optical component as the above portion of the multi-layer film, the optical component having a good optical characteristic can be formed. Further, since the thickness of only a portion of the multi-layer film is measured, the film thickness control can be easily performed. As a result, it is possible not only to produce an optical component having a good optical characteristic but also to produce a plurality of optical components without a variation in optical characteristic therebetween.
In the apparatus according to the first aspect of the present invention, preferably, the measurement means measures a transmittance of the optical component, and the control means terminates the film formation by the film formation means at the portion of the multi-layer film when the measured transmittance of the optical component is changed to be decreased.
In the method according to the second aspect of the present invention, preferably, the measurement step includes the step of measuring a transmittance of the optical component; and the control step includes the step of terminating the film formation at the portion of the multi-layer film when the measured transmittance of the optical component is changed to be decreased.
With these configurations, the transmittance of the optical component is measured (by the measurement means), Id and the film formation (by the film formation means) at the portion of the multi-layer film is terminated when the measured transmittance of the optical component is changed to be decreased. As a result, an optical component, which is composed of the multi-layer film exhibiting a good optical characteristic formed on the base, can be obtained.
The above preferable apparatus, specifying the transmittance as the optical characteristic, according to the first aspect of the present invention, may further include removal means for removing the layer portion formed during a period of time from a time point when the increase/decrease of the measured transmittance of the optical component is stopped to a time point when the measured transmittance is changed to be decreased.
The above preferable method, specifying the transmittance as the optical characteristic, according to the second aspect of the present invention, may further include a removal step of removing a layer portion formed during a period of time from a time point when the increase/decrease of the measured mean light transmittance of the optical component is stopped to a time point when the measured mean light transmittance is changed to be decreased.
With these configurations, since a layer portion formed during a period of time from a time point when the increase/decrease of the measured transmittance of the optical component (by the measurement) is stopped to a time point when the measured transmittance is changed to be decreased is removed (by the removal means), the layer thickness can be finely adjusted. As a result, it is possible to produce an optical component capable of more accurately exhibiting a good optical characteristic.
In the apparatus according to the first aspect of the present invention, preferably, the control means controls a thickness of one layer of the plurality of alternately stacked layers, the one layer having a higher refractive index and being positioned near the uppermost surface remotest from the base.
In the method according to the second aspect of the present invention, preferably, the control steps include the step of controlling a thickness of one layer of the plurality of alternately stacked layers, the one layer having a higher refractive index and being positioned near the uppermost surface remotest from the base.
With these configurations, a thickness of one layer of the plurality of alternately stacked layers constituting the multi-layer film is controlled (by the control means). The one layer has a higher refractive index and is positioned near the uppermost surface remotest from the base. It has been found by the present inventors that, of the plurality of alternately stacked layers, one layer having a higher refractive index and being positioned near the uppermost surface remotest from the base exerts a large effect on the optical characteristic of the optical component. As a result, by controlling the thickness of such a layer (by the control means), it is possible to produce an optical component having a good optical characteristic.